In article , Mortimer
writes
I wonder if some of the colour cast of moonlight pictures was down to
the infamous "reciprocity failure" that film is prone to in very low
light, whereby the normal rule that halving the aperture requires a
doubling of shutter speed no longer works and the three emulsions
respond differently to light. Mind you I once took some very long
exposure shots (eg f11 for 2 mins on 200 ASA) of Christmas lights and
other street scenes and didn't see any colour cast that couldn't simply
be attributed to the non-tungsten street lights.

I forgot this was cross-posted away from UTB.

It's crossed-curves, not just reciprocity failure. R.F. means you have
to increase long exposure times by a compensation factor (as you say),
but of itself it won't cause colour casts.

The cast comes from a large number of other factors, including the
illumination, temperature of the film, the change in UV content of the
light (often filtered out however), and the fact that RP doesn't affect
the emulsions identically for all of the colours.

If the above is a bit rough, I've forgotten much of it. I need to dig
out my books on colour processes...

--
SimonM
----- TubeWiz.com -----
Video making/uploading that's easy to use & fun to share
Try it today! (now with DFace blurring)